Ninety-nine percent of the radiation from the sun consists of visible light, ultraviolet light.true or false?

A 26 foot ladder is lowered down a vertical wall at a rate of 3 feet per minute. The base of the ladder is sliding away from the

lakkis [162]

Answer:

(i) 7.2 feet per minute.

(ii) No, the rate would be different.

(iii) The rate would be always positive.

(iv) the resultant change would be constant.

(v) 0 feet per min

Explanation:

Let the length of ladder is l, x be the height of the top of the ladder from the ground and y be the length of the bottom of the ladder from the wall,

By making the diagram of this situation,

Applying Pythagoras theorem,

$l^2 = x^2 + y^2-----(1)$

Differentiating with respect to t ( time ),

$0=2x\frac{dx}{dt} + 2y\frac{dy}{dt}$ ( l = 26 feet = constant )

$\implies 2y\frac{dy}{dt} = -2x\frac{dx}{dt}$

$\implies \frac{dy}{dt}=-\frac{x}{y}\frac{dx}{dt}$

We have,

$y = 10, \frac{dx}{dt}= -3\text{ feet per min}$

$\frac{dy}{dt}=\frac{3x}{10}-----(X)$

(i) From equation (1),

$26^2 = x^2 + 10^2$

$676=x^2 + 100$

$576 = x^2$

$\implies x = 24\text{ feet}$

From equation (X),

$\frac{dy}{dt}=\frac{3\times 24}{10}=7.2\text{ feet per min}$

(ii) From equation (X),

$\frac{dy}{dt}\propto x$

Thus, for different value of x the value of $\frac{dy}{dt}$ would be different.

(iii) Since, distance = Positive number,

So, the value of y will always a positive number.

Thus, from equation (X),

The rate would always be a positive.

(iv) The length of the ladder is constant, so, the resultant change would be constant.

i.e. x = increases ⇒ y = decreases

y = decreases ⇒ y = increases

(v) if ladder hit the ground x = 0,

So, from equation (X),

$\frac{dy}{dt}=0\text{ feet per min}$

3 0

3 years ago

Physics question!!!

lesantik [10]

Answer:

4.5 metres

Explanation:

Using Hooke's Law ( $F\propto x$ )

We need to find the spring constant of the bungee cord with the given extension and force, we can do this by substituting in known values.

$600=3k\\k=200$

Now we have found the spring constant of the bungee cord, we can substitute it in for the a different force. As the cord is the same we can use the same spring constant.

$900=200x\\x=4.5$

5 0

2 years ago

Explain how a rotating electric fan might be used to model the atom. explain how the rotating fan is unlike an atom.

quester [9]

A fan may be used to model an atom because the fan blades form something similar to a electron cloud. But there is really nothing to model the neutrons and protons. Also the fan is flat like where an atom is more 3-D sphere-like.

hope this helps

Ur welcome

have a great day (:

3 0

3 years ago

List 5 plants or animals that the emporer penguin eats

patriot [66]

Answer:

Emperor penguins are near the top of the Southern Ocean’s food chain. They have a varied menu that changes with the season. Some prey items are more important than others. One of the most frequently eaten prey species is the Antarctic silverfish Pleuragramma antarcticum. They also eat other fish, Antarctic krill and some species of squid. Most prey items are small. Since they are very cold when ingested, their small size makes it easier to bring food up to body temperature to digest it.

6 0

2 years ago

A 40.0 kg physics student at rest on a frictionless rink throws a 3.0 kg box, giving the box a velocity of 8.0 m/s. Which statem

zvonat [6]

Answer: (b)

Explanation:

Given

mass of Student M=40 kg

mass of box m=3 kg

velocity of box v=8 m/s

suppose u is the velocity of the student after the throw

As there is no external force is applied so momentum is conserved

Initial momentum=final momentum=0

0=Mu+mv

Mu=-mv

$u=-\frac{3}{40}\times 8=-\frac{3}{5}\\u=-0.6\ m/s$

Here negative sign indicates the velocity is opposite in direction i.e. opposite to the direction of the box

6 0

2 years ago